question about ph

LunchBox

LunchBox

Me fail english? that's unpossible!
Feb 7, 2006
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Kalamazoo, MI
so I did a test this morning of my tank water, some tap water that stood out overnight and water right out of the tap. apparently when my tap water sits for any length of time the ph goes up about 0.9 and I'm not sure why it would do that. Does anyone have any ideas as to what things might cause something like that?

here are the readings:
tank water - 8.0
tap water aged 1 full day - 8.0
fresh tap water - 7.1

any insight anyone can give would be appreciated. 8.0 is not a big deal right now, but I am just curious as to what would make it go up like that.

Thanks!
 
Really doesn't make sense to me. It should actually decline.

But here's a completely wild, outlandish thought that I have.


Maybe the higher amount of compressed air in freshly drawn tap water is affecting the test results? See, with all of that atmospheric air in the water, you will have a higher amount of CO2, thus lowering the pH.
 
possible. I'm on city water with a softener so maybe it has something to do with the softener salt too. At least my tank matches the tap water that sat out though ;) I ran the fresh tap water test twice now, once with filling the tube right from the faucet and once where I filled a bowl and dipped the tube in the bowl to fill it (just in case air in the water coming right out of the faucet was skewing the results) and the results are the same.

I'll have to see if I can get a hold of some data from public works to see what the water parameters are supposed to be. I could probably try to test water before it gets to the water softener (I tihnk my utility sink is pre-softened) and see how that comes out too just for curiosity's sake ;)
 
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it has to do with carbon dioxide in your water. under pressure, the CO2 is in equillibrium with carbonic acid. when the water comes out of the tap and aerated, CO2 is driven off and the equillibrium shifts toward the carbonate side. this drives the ph up.
 
liv2padl said:
it has to do with carbon dioxide in your water. under pressure, the CO2 is in equillibrium with carbonic acid. when the water comes out of the tap and aerated, CO2 is driven off and the equillibrium shifts toward the carbonate side. this drives the ph up.
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An entire point shift is pretty much average, correct? Mine will go from 7.4 to 8.4 over night and gassed off.

In order to correct an "overdose" of CO2 (darn needle valve shifted or bumped or whoknowswhat!) I had to run three bubble wands in one of my tanks overnight. pH went from at least 6.0-6.4 up to 8.0 in the morning when I took the wands out.

Was kinda cool since I've never had my pH that high unless I use crushed coral to make it that high.

Roan
 
I guess I learn something new every day ;)

good to know that a 1 point shift is normal. I had no idea there was enough CO2 in the water lines to make a difference like that.

so knowing that, tap water will gain 1 point overnight after coming out the tap, then the ph will gradually drift down over time naturally? but then a weekly water change will probably make that drift not as noticeable I would imagine since new tap water would be replacing a portion of the old, thus raising the ph a bit again. good stuff to know! I'm beginning to wonder if I'm in the wrong business and should have become a chemist ;) this stuff is really interesting :)
 
The shift can and does change seasonally. In most areas it is maximized in winter as the water is coldest then and can hold more dissolved gases.

But there is no such thing as "it should go up" or "it should go down" - that is totally a function of the local water source and its processing.
 
RTR said:
The shift can and does change seasonally. In most areas it is maximized in winter as the water is coldest then and can hold more dissolved gases.

But there is no such thing as "it should go up" or "it should go down" - that is totally a function of the local water source and its processing.
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What causes it to go down, RTR? I can understand how it would go up with gas release, but down?

Roan
 
Many relatively soft water area utilities use short-lived phosphate buffers (yes, the same stuff sold for "buffering" tanks) to keep the water alkaline and thus protect the copper pipes. This water tends to come out of the tap at least mid-7s if not higher, then drop to low 7s or below after a day or two or three.

You utility can be your friend - in this country they are required by EPA to inform their clients - but you do need a bit of background or Googling to catch on to what it all means directly on the hobby tanks. The county next closer to DC from us (Montgomery) uses Potomac water (as does DC and parts of NVA), so must add buffers to avoid pinhole leaks in the residences there. Aged water from such systems drops in pH rather than going up. Pressurized surface water does not carry the CO2 load of deep-well water in this area.
 
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